Image device



A. E. ANDERSON ETAL 3,254,252

IMAGE DEVICE May 31, 1966 Filed Jan. 24, 1962 Fig. I

WITNESSES INVENTORS Arthur E. Anderson and Gerhard W. Goetze W J A United States Patent 3,254,252 IMAGE DEVICE Arthur E. Anderson, Penn Hills, and Gerhard W. Goetze, Monroeville, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 24, 1962, Ser. No. 168,416 5 Claims. (Cl. 313-94) This invention relates to image producing systems of the type in which a radiation image received on an input screen produces an amplified output.

The present invention is particularly applicable to the field of X-ray image intensification. It is well known that present X-ray image intensifier tubes have insufficient brightness gain to permit the use of the minimum dosages required to realize the full resolution capability. It can also be shown that practical considerations of total voltage and field size prevent the realization of the required gain in a single stage device.

It is, therefore, an object of the present invention to provide an improved type of image pick-up tube.

Another object is to provide improved multiple stage image tube.

A further object is to provide amplification of the electron image prior to bombardment of the target electrode.

A still further object is to provide an improved image tube having a large area input screen and a small area output target.

Stated briefly, the prevent invention describes an image intensification tube having a large area input screen. Radiation impingent upon the input screen results in an electron image corresponding thereto which is minified and directed onto an electron amplification electrode. The amplified electron image resulting from this latter electrode is then directed onto an output target to provide an output image of increased brightness.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference maybe had to the accompanying drawings, in which:

FIG. 1 is an elevational view in section of a device embodying the present invention; and,

. FIG. 2 is an enlarged sectional view of one form of electron amplification electrode which may be used in accordance with the present invention.

Referring now to FIG. 1, an electron discharge tube -is'shown comprising an envelope having an enlarged cylindrical portion 12 and a restrict-ed cylindrical portion 14. The envelope 10 is made of a suitable material such as glass. The enlarged portion 12 is closed off by an end plate 16 which may be formed as an integral part of the envelope 10 while the restricted portion 14 is closed off by an end plate 19.w-hich is hermetically sealed to the portion 14.

,An input screen 20 is positioned near to the end plate 16. As the illustrated embodiment is designed for X-ray image intensification, the input screen 20 includes a member 22 of X-ray sensitive material, for example zinc cadmium sulfide. An X-ray image impingent upon one surface of the member 22 causes the emission of a light image corresponding thereto from the opposite surface of the member 22. The input screen 20 also includes a photocathode 24, of suitable material such as cesium antimony, which is in close optical contact with the X- ray sensitive layer 22. The photocathode 24 receives the light image from the layer 22 and emits an electron image which corresponds to the light image impingent thereon. A barrier layer 25, which may be made of glass, is interposed between the layer 22 and the photocathode 24 to prevent actual physical contact of these latter two elements. The nature of the input screen 20, that is, one which changes an X-ray image to a light image and then to an electron image is one which is well known in the art. In the present example, the input screen 20 is approximately six inches in diameter.

An electron multiplication means 32 is positioned remotely from the input screen 20 within the restricted portion 14. In the preferred embodiment, the multiplication means 32 is a transmission-secondary emission type dynode; that is, a dynode which emits secondary electrons from one surface thereof in response to electron bombardment of the other surface thereof. The construction of the dynode 32 may best be understood with reference to FIG. 2. Dynode 32 comprises a thin layer of electrically conductive material 34, .for example aluminum, having a thickness in the order of .05 micron. A layer 35 of material exhibiting transmission-secondary emission properties, for example potassium chloride, barium fluoride and magnesium oxide, is deposited upon the conducting layer 34. The layer 35 is preferably in the form of a spongy or porous deposit having a density of less than ten percent of the bulk or normal density of the material of which it is composed. The layer 35 may have a thickness in the range of from ten to one hundred microns. It is desirable that the above structure be secured to a support ring 33 which is of suitable material such as copper or nickel to provide mechanical support for the dynode structure. For a more complete explanation and description of dynodes of this nature, reference is made to US. Patent 3,197,662, filed March 11, 1960, entitled Electron Discharge Devices by Robert J. Sc-hneeberger and which is assigned to the assignee of the present invention. In the embodiment illustrated, the dynode 32 has a diameter of approximately 1.2 inches.

In accordance with the present invention, means are provided intermediate the input screen 20 and the dynode 32 for the minificat-ion of the electron image emitted from the screen 20 onto the dynode 32. The minification means is in the form of an electrostatic lens system 26 which comprises a plurality of cylindrically shaped members 27 31 of electrically conductive material. The members 27-31 are of diminishing physical size and are connected by leads 45-49 to a source of power which is external to the envelope 10. The members 2731 are maintained at different values of potential and in accordance with the ratio of sizes of the input screen 20 to the dynode 32 pro- ;nde a; mmification or demagnification in the ratio of about The minified electron image which is directed onto one surface of the dynode 32 results in the electrons being secondarily emitted from the other surface thereof. These secondarily emitted electrons are directed onto an output target 18 which may be approximately the same size as the dynode 32. Output target 18 includes a con-' ducting layer of suitable light transmissive material 21, such as tin oxide, onto which is deposited a layer 23 of suitable flourescent material, such as zinc cadmium sulphide, which emits light in the visible region in response to electron bombardment.

A suitable focusing system may be provided around the restricted portion of the envelope 14 for focusing the electrons between the dynode 32 and the target 18. In

. the specific embodiment, the focusing device is shown as a permanent magnet 40 which provides a longitudinal magnetic field Within the envelope.

A control grid 42 of large open area is positioned intermediate the dynode 32 and the target 18. The spacings between the dynode 32 control grid 42, and target Patented May 31, 1966' 18 are adjusted to best obtain focus of the amplified image with the selected operating voltages and magnetic focusing field. It is also possible to utilize the grid 42 to limit the potential to which the surface of the layer 35 can rise. The grid 42 should be held at a voltage of about to 200 volts positive with respect to the conducting coating 34.

The requisite potential for the elements within the envelope 10 may be obtained from a potentiometer or other suitable device. In the specific device shown in FIG. 1, we have utilized a battery 38 having its negative terminal connected by means of a conductor 52 to the input screen and its positive terminal connected by a lead 53 to the conductive layer 21 of the target 18, A resistor 39 connected in shunt with the battery 38 provides means whereby the remaining elements within the envelope 12 may be connected, by means of leads -51 to potentials of intermediate values.

In one specific example of a tube built in accordance with the present invention, it was found that a total potential difference of approximately 8 kilovolts between the input screen 20 and the dynode 32 accelerated the primary electrons striking the dynode film to an energy which would produce the maximum number of secondaries from the dynode. In this example, the control grid 42 was held slightly positive with respect to the dynode 32 and a potential difference of approximately 20 kilovolts was placed between the dynode 32 and the target 18. The 20 kilovolt potential difference between the dynode 32 and the target 18 serves to accelerate the secondarily emitted electrons onto the output phosphor to greatly enhance the brightness. In the arrangement described, it was found that the brightness gain was 15 times that of a conventional single stage tube operated with the same total voltage applied.

While there has been shown and described what is at present considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. For example, if it were desired to operate the device as a visual image pick-up tube, the X-ray sensitive layer 22 of the input screen could be eliminated. Also, other forms of electron multiplication other than transmissive-secondary emission type dynodes may be employed. Included in these would be an electron emissive photocathode in contact with a phosphor screen which emits secondary electrons in response to primary electron bombardment in a ratio of greater than one to one. In addition, fiber optic means could be utilized as either a radiation input or output for the device.

It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

We claim as our invention:

1. An image tube comprising an envelope, cathode means within said envelope for the production of an electron image in response to a radiation image thereon, dynode means including a porous layer of material spaced from said cathode means for receiving said electron image, said porous layer exhibiting transmission-secondary emission properties to provide the emission of secondary electrons on one surface of said dynode in response to electron bombardment of the opposite side, said porous layer having a density less than ten percent of the bulk density of said material, means intermediate said cathode means and said dynode means for the minification of said electron image from said cathode means, and means for receiving said secondarily emitted electrons from said dynode.

2. An image tube comprising an evacuated envelope, cathode means responsive to incident radiation for the production of an electron image disposed at one end of said envelope, dynode means including a porous layer of material disposed within said envelope and spaced from said cathode means for receiving the electron image from said cathode means, said porous layer having a density less than ten percent of the bulk density of said material and exhibiting transmission-secondary emission properties, means intermediate said cathode means and said dynode means to demagnify the electron image, and target means disposed at the other end of said envelope for receiving electrons from said dynode means.

3. An electrical device comprising an envelope, an input screen responsive to X-ray radiation to produce a light image disposed at one end of said envelope, a photocathode positioned in close optical contact with said input screen for producing an electron image corresponding to said light image, a dynode including a porous layer of material having a density of less than ten percent of the bulk density of said material spaced from said photocathode for receiving said electron image, said dynode exhibiting transmission-secondary emission properties to provide the emission of secondary electrons on one side of said dynode in response to electron bombardment of the opposite side thereof, means intermediate said photocathode and said dynode for the minification of said electron image from said photocathode, and target means for receiving electrons from said dynode.

4. An image tube comprising a photo emissive cathode for the production of an electron image in response to a radiation image thereon, dynode means spaced from said cathode for receiving said electron image, said dynode including a porous layer of material having a density of less than ten percent of the bulk density of said material exhibiting the property of secondary electron emission rom one surface in response to electron bombardment of the other surface thereof, said cathode having a surface area approximately 25 times that of said dynode, minification means intermediate said cathode and said dynode to focus said electron image onto said dynode and target means for receiving the secondarily emitted electrons from said dynode.

5. An image device comprising electron emissive means for the production of an electron image in response to a radiation image impingent thereon, electron multiplication means positioned in a spaced relationship with respect to said input screen for receiving electrons from said electron emissive means, said electron multiplication means including a porous layer of material exhibiting transmission-secondary emission properties, a minifying electrostatic lens system intermediate said electron emissive means and said electron multiplication means, target means spaced from said electron multiplication means for receiving electrons therefrom, and grid means intermediate said porous layer and said target means, and means for supplying an electrical potential to said grid whereby the potential to which said porous layers can rise is limited.

References Cited by the Examiner UNITED STATES PATENTS 2,612,610 9/1952 Marshall et al 313-68 X 2,898,499 8/1959 Sternglass et a1 313-67 X 2,928,969 3/ 1960 Schneeberger 313- 3,026,437 3/1962 Niklas 3l365 JOHN W. HUCKERT, Primary Examiner.

GEORGE N. WESTBY, Examiner.

R. POLISSACI-I, Assistant Examiner 

1. AN IMAGE TUBE COMPRISING AN ENVELOPE, CATHODE MEANS WITHIN SAID ENVELOPE FOR THE PRODUCTION OF AN ELECTRON IMAGE IN RESPONSE TO A RADIATION IMAGE THEREON, DYNODE MEANS INCLUDING A POROUR LAYER OF MATERIAL SPACED FROM SAID CATHODE MEANS FOR RECEIVING SAID ELECTRON IMAGE, SAID POROUS LAYER EXHIBITING TRANSMISSION-SECONDARY EMISSION PROPERTIES TO PROVIDE THE EMISSION OF SECONDARY ELECTRONS ON ONE SURFACE OF SAID DYNODE IN RESPONSE TO ELECTRON BOMBARDMENT OF THE OPPOSITE SIDE, SAID POROUS LAYER HAVING A DENSITY LESS THAN TEN PERCENT OF THE BULK DENSITY OF SAID MATERIAL, MEANS INTERMEDIATE SAID CATHODE MEANS AND SAID DYNODE MEANS FOR THE MINIFICATION OF SAID ELECTRON IMAGE FROM SAID CATHODE MEANS, AND MEANS FOR RECEIVING SAID SECONDARILY EMITTED ELECTRONS FROM SAID DYNODE. 